Periods of spontaneous rhythm in the turtle heart and their bearing upon paroxysmal tachycardia.

Abstract

In frogs'hearts filled with mammalian serum and ligated between sinus venosus and auricles, or at other points, Luciani 1 observed and recorded periods of spontaneous rhythm separated by intervals of quiescence. We have obtained myograms and electrograms of the same phenomenon in turtle hearts perfused with strongly buffered, oxygenated physiological saline solutions at various H-ion concentrations. A typical period of auricular origin recorded with the string galvanometer is given in Figure 1. It will be noted that there is a rapid acceleration in the rhythm and then a more gradual retardation until the period ends.

Certain peculiarities in the time relations of the cycles during a period, and of the intervals between spontaneously initiated periods, suggested that their origin and course might readily be explained on the basis of a few well supported assumptions. First, that the impulses are discharged from an ectopic focus. Since the sinus is ligated off and since the time relations and electrograms seem to prove that the period is not due to circus contractions, there must be an ectopic focus. Second, that the impulse discharge deperids upon the attainment of a sufficient degree of excitahility in the focus. This is probable, for although highly excitable tissues are not necessarily spontaneously active, no one is likely to deny that the excitability is one determining factor where conditions are otherwise favorable to inipulse discharge. 2 Third, that the returning excitalility after each discharge passes through a supernormal phase. Adrian 3 has shown that nerve and muscle bathed in faintly acid solutions do show a supernormal recovery, i. c., the excitability for a certain time after the response exceeds the resting (and depressed) excitability. Fourth, that there is a “treppe” in excitability for the first several recoveries of the period.